Pressure-sensitive copying sheet utilizing stabilized crystal violet lactone, method of making and method of making composition

ABSTRACT

A chlorinated diphenyl solvent solution of Crystal Violet Lactone as well as an emulsion for use in pressure-sensitive copying papers which contain microcapsules wherein said solvent solution is encapsulated as an internal liquid phase may be substantially prevented from becoming blue stained by the action of light by incorporating at least 0.5 percent, preferably 2.5-10 percent by weight based on the amount of Crystal Violet Lactone of 2-(p,p&#39;&#39;-bis(dimethylamino)benzhydrol)-5-dimethylaminobenzoic acid in said solvent solution. In a pressure-sensitive copying paper, the rear surface of a writing sheet being intended to be brought into contact with the clay-coated surface of a recording sheet, which has been coated with the aforesaid emulsion, does not substantially tend to become blue stained on exposure to the sunlight even for a considerably long period of time, and hence is of great commercial usefulness.

United States Patent Orita et al.

PRESSURE-SENSITIVE COPYING SHEET UTILIZING STABILIZED CRYSTAL VIOLET LACTONE,

METHOD OF MAKING AND METHOD OF MAKING COMPOSITION Michio Orita; Masakichi Yahagi, both of Tokyo, Japan Assignee: Nisso Kako Co., Ltd., Tokyo, Japan Filed: Apr. 27, 1970 Appl.No.: 32,373

Inventors:

References Cited UNITED STATES PATENTS 2/1962 Bakan et al. .....117/36.2

[ 1 Feb. 15,1972

3,501,331 3/1970 Kimura et al. ..1 17/362 Primary Examiner-Murray Katz Art0meyWaters, Roditi, Schwartz & Nissen [57] ABSTRACT A chlorinated diphenyl solvent solution of Crystal Violet Lac tone as well as an emulsion for use in pressure-sensitive copying papers which contain microcapsules wherein said solvent solution is encapsulated as an internal liquid phase may be substantially prevented from becoming blue stained by the action of light by incorporating at least 0.5 percent, preferably 25-10 percent by weight based on the amount of Crystal Violet Lactone of 2-[p,p'-bis(dimethylamino)benzhydrol]-5- dimethylaminobenzoic acid in said solvent solution. In a pressure-sensitive copying paper, the rear surface of a writing sheet being intended to be brought into contact with the claycoated surface of a recording sheet, which has been coated with the aforesaid emulsion, does not substantially tend to become blue stained on exposure to the sunlight even for a considerably long period of time, and hence is of great commercial usefulness.

7 Claims, No Drawings PRESSURE-SENSITIVE COPYING SHEET UTILIZING STABILIZED CRYSTAL VIOLET LACTONE, METHOD OF MAKING AND METHOD OF MAKING COMPOSITION This invention relates to a method of preventing a chlorinated diphenyl solvent solution of Crystal Violet Lactone from becoming blue stained under the action of light. More particularly, the invention pertains to a method of preventing said solution encapsulated into microcapsules for use in pressure-sensitive copying papers present in an emulsion formed from said solution from becoming blue stained on exposure to the sunlight; a writing sheet of a pressure-sensitive copying paper, the rear surface of which has been coated with said microcapsules present in said emulsion and dried; and to a method of making pressure-sensitive copying papers.

I11 (CH-D2 (I) Crystal Violet Lactone represented by the above formula is a colorless substance in itself, but it becomes blue stained when brought into contact with an electron-accepting substance, for example, acid clay and the like. Because of this property, Crystal Violet Lactone is being widely utilized as a color-forming substance in the field of noncarbon pressuresensitive copying papers. In application, Crystal Violet Lactone is first dissolved in a solvent, such as chlorinated diphenyl or the like. From the resulting solution, an emulsion having microcapsules in which said solvent solution has been encapsulated as an internal liquid phase is prepared. The rear surface of a writing sheet of paper is coated with the emulsion thus prepared, and the coated writing sheet is dried. Separately, a recording sheet of paper is coated on its surface with acid clay, and the coated recording sheet is dried. The writing sheet is then superposed on the recording sheet so that the coated surface of the former is brought into direct contact with the clay-coated surface of the latter. To the assembly, localized pressures are applied by writing certain words or figures on the surface of writing sheet, whereupon the microcapsules at the points of the rear-coated surface of the writing sheet to which the localized pressures have been applied are destroyed. The solution which flows out from each destroyed microcapsule contacts the acid clay on the surface of the recording sheet, whereupon corresponding words or figures are developed in blue color on the surface of the writing sheet.

Crystal Violet Lactone is produced usually by oxidizing with potassium permanganate in an alkaline environment 2-[p,pbis(dimethylamino)benzhydrol-5-dimethylaminobenzoic acid (hereinafter referred to as acid (11)) having the following formula:

COOH

Crystal Violet Lactone thus obtained is relatively stable under the influence of light and becomes scarcely blue stained when it is present in a crystalline form. This substance, however, easily tends to become sensitive to light when dissolved in a solvent, for example, chlorinated diphenyl or the like, or the like media. Thus, the substance in the form of a solution is liable in most cases to discoloration to a blue color on irradiation. Such discoloration takes place in microcapsules for use in pressure-sensitive copying papers, into which said solution has been encapsulated as an internal liquid phase, as well as on the rear surface of a writing sheet of an assembly of pressuresensitive copying papers, onto which said microcapsules present in an emulsion have been applied. Accordingly, pressure-sensitive copying papers prepared according to conventional methods by utilizing Crystal Violet Lactone solution are of little commercial usefulness in view of the disadvantage that the coated rear surface of the writing sheet is liable to such discoloration, whereby the external appearance of the article is degraded, and that the color-forming effect of the article is adversely affected in practical application due to such discoloration phenomenon.

On the other hand, however, extensive studies and investigation carried out by the present inventors on a method of preventing a Crystal Violet Lactone solution in a solvent from becoming blue stained by the resulted in the finding that the desired prevention can be achieved by adding an appropriate amount of acid (11) to a 5 substantially Crystal Violet Lactone solution in a solvent. Further, it has been found that microcapsules present in an emulsion for use in pressure-sensitive copying papers, which enclose as an internal liquid phase said Crystal Violet Lactone solution can be prevented likewise from becoming blue stained on exposure to light. Thus, we have succeeded in establishing the present invention on the basis of the above findings.

Table 1 given below is to demonstrate the effect of the present invention with reference to the results of discoloration test as set forth therein. The test was conducted in the following manner:

To a 0.5 percent solution of Crystal Violet Lactone in dichlorophenyl was added acid (II) in varied proportions based on Crystal Violet Lactone as set forth in Table 1. Each of the resultant solutions was exposed to the sunlight in accordance the exposure schedule as set forth in Table l to investigate the degree of discoloration of each test solution. The results were as shown in Table 1.

TABLE 1 (percent by weig 1 3 6 12 24 X X X X X X s X X a s a A 8 A X X g g See following table:

Discoloration index Degree of discoloration X Deeply blue-stained. A Blue-stained.

Very slightly blue-stained. 8 No change.

As can be clearly seen from the above Table 1, an addition of 0.5 percent of acid (II) begins to exhibit the effect more or less, but this is of course of little real use. Addition of 2.5-10 percent of acid (H) is therefore most preferred both from technical and economical points of view. If an excessively large amount of acid (H) is added, color formation is undesirably decreased in color intensity when Crystal Violet Lactone is brought into contact with acid clay or with other electron acceptors.

In the step of dissolving Crystal Violet Lactone and acid (II) in chlorinated diphenyl according to the method of the not always be mixed together in their respective forms. For instance, in carrying out the oxidation of acid (II) to give Crystal Violet Lactone, an appropriate amount of the former can be contained in the resulting oxidation product, i.e., Crystal Violet Lactone, by controlling the oxidation conditions to be employed for the oxidation of acid (H).

The addition of acid (ll) is effective not only in preventing a Crystal Violet Lactone-chlorinated diphenyl solution from becoming blue stained by the action of light but also in the case of said solution with which other color-forming substances for use in pressure-sensitive copying paper other than Crystal Violet Lactone, e.g., Benzoyl Leuco Methylene Blue, or ultraviolet ray-absorbing substances coexist. The addition of acid (II) is effective likewise in the case where the solvent comprises a solvent other than chlorinated diphenyl, for example, vegetable oils, mineral oils or the like solvents, in addition to the chlorinated diphenyl.

Microcapsules for use in pressure-sensitive copying papers used in the present invention, which enclose the aforesaid mixed solution as an internal liquid phase, may be prepared according to conventional methods commonly employed therefore without necessitating any special steps or specific conditions.

For a fuller understanding of the present invention, reference should be had to the following examples which are given merely to illustrate the invention and are not to be construed in a limiting sense.

Example 1 5.0 g. of Crystal Violet Lactone and 0.25 g. ofacid (II) were mixed together. The resulting mixture was dissolved with heating in 100 g. of dichlorodiphenyl to give a solution (referred to as solution A). Separately, 5.0 g. of Crystal Violet Lactone alone was dissolved with heating in 100 g. of dichlorodiphenyl to give a solution (referred to as solution B). Both solutions A and B were pale yellow in color. On exposure to the sunlight, solution B became deeply blue stained in 20 minutes, while solution A remained unchanged even after the lapse of 24 hours.

EXAMPLE 2 Two grams of Crystal Violet Lactone and 0.05 g. ofacid (II) were dissolved with heating in 40 g. of trichlorodiphenyl to give a solution (referred to as solution A). On the other hand, 5.0 g. of gelatine having an isoelectric point of 8.0 was dissolved in 800 cc. of water, and the resulting solution was controlled at 50-60 C. to pH 8.0 with a 5 percent aqueous sodium hydroxide solution (the resultant solution being referred to as solution B). Solution A was poured into solution B while stirring at high speed to emulsify the resulting mixed solution. To the resulting emulsified mixture was added with stirring 80 cc. of a solution of g. of gum arabic in water, which had been adjusted to pH 8.0. While continuing the stirring, the resulting mixture was adjusted to pH 5.0 with a 5 percent acetic acid, and 250 cc. of water was added thereto. The resulting mixture was further adjusted to pH 4.4 with acetic acid. Thereafter, the mixture was charged with l.9 g. of a 37 percent formation and cooled to 10 C. Sub sequently, the resulting mixture was adjusted to pH 9.0 with a 5 percent aqueous sodium hydroxide solution, and was then allowed to stand for several hours, whereby a white-colored emulsion was obtained. The emulsion thus obtained contained very fine capsulated particles (so-called microcapsules) with a film formed from the gelatine and gum arabic, in which a solution of Crystal Violet Lactone and acid (ll) in trichlorodiphenyl has been contained as an internal liquid phase.

A paper sheet used as a writing sheet was coated on its rear surface with the emulsion and dried. The coated rear surface of the sheet was superposed on the acid clay-coated dried surface ofa paper sheet used as a recording sheet. To the resulting assembly, localized pressures were given by writing words on the surface of the writing sheet, whereupon corresponding words in blue color developed on the clay-coated surface of the recording sheet.

A paper sheet, which had been coated on one surface with this emulsion, took a considerably long period of time before the coated surface thereof became blue stained on exposure to the sunlight. While the coated surface of a paper sheet, which had been coated on one surface with the emulsion prepared in the same manner as above except that acid (II) was not used in the aforesaid solution A, became blue stained in a short period oftime on exposure to the sunlight.

EXAMPLE 3 A microcapsule-containing emulsion was prepared in the same procedure as described in Example 2 except that a solution of 2.0 g. of Crystal Violet Lactone, 0.1 g. of acid (ll) and 2.0 g. of Benzoyl Leuco Methylene Blue in 40 g. of

trichlorodiphenyl had been used in place of solution A used in Example 2. A paper sheet was coated on one surface with the emulsion thus prepared and the coated sheet was dried. The coated surface of the paper sheet became very slightly blue stained on exposure to the sunlight even for a considerably long period of time.

What we claim is:

1. A method of preventing a chlorinated diphenyl solvent solution of Crystal Violet Lactone for use in pressure-sensitive copying paper from becoming blue stained by the action of light, which comprises incorporating at least 0.5 percent by weight based on the amount of Crystal Violet Lactone of 2- [p,p'-bis(dimethylamino)benzhydrol1-5- dimethylaminobenzoic acid in said solvent solution.

2. A method according to claim 1, wherein the solvent solution is an emulsion which contains individually separate, fine capsules wherein said solvent solution is encapsulated as an internal liquid phase.

3. A method according to claim 1, wherein the solvent solution of Crystal Violet Lactone contains a member or members selected from the group consisting of color-forming substances for use in pressure-sensitive copying paper other than Crystal Violet Lactone, and ultraviolet ray-absorbing substances.

4. A method according to claim 1, wherein the chlorinated diphenyl solvent is a mixed solvent of chlorinated diphenyl with a member or members selected from the group consisting of solvents other than chlorinated diphenyl, vegetable oils and mineral oils.

5. In a process for making a pressure-sensitive copying paper, a method of preparing a writing sheet of the copying paper, which comprises coating the rear surface of the writing sheet which is intended to be brought into contact with the clay-coated surface of a recording sheet with an emulsion prepared according to claim 2 so as to provide a dry, thin, uniform, substantially white, solid to touch, not sticky or tacky donor layer thereon.

6. A pressure-sensitive copying paper, of which the rear surface of a writing sheet being intended to be brought into contact with the clay-coated surface ofa recording sheet has been treated according to the method of claim 5.

7. A method according to claim 1 wherein the amount of 2- [p,p-bis(dimethylamino)benzhydrol1-5- dimethylaminobenzoic acid is from 2.5 to weight.

10 percent by 

2. A method according to claim 1, wherein the solvent solution is an emulsion which contains individually separate, fine capsules wherein said solvent solution is encapsulated as an internal liquid phase.
 3. A method according to claim 1, wherein the solvent solution of Crystal Violet Lactone contains a member or members selected from the group consisting of color-forming substances for use in pressure-sensitive copying paper other than Crystal Violet Lactone, and ultraviolet ray-absorbing substances.
 4. A method according to claim 1, wherein the chlorinated diphenyl solvent is a mixed solvent of chlorinated diphenyl with a member or members selected from the group consisting of solvents other than chlorinated diphenyl, vegetable oils and mineral oils.
 5. In a process for making a pressure-sensitive copying paper, a method of preparing a writing sheet of the copying paper, which comprises coating the rear surface of the writing sheet which is intended to be brought into contact with the clay-coated surface of a recording sheet with an emulsion prepared according to claim 2 so as to provide a dry, thin, uniform, substantially white, solid to touch, not sticky or tacky donor layer thereon.
 6. A pressure-sensitive copying paper, of which the rear surface of a writing sheet being intended to be brought into contact with the clay-coated surface of a recording sheet has been treated according to the method of claim
 5. 7. A method according to claim 1 wherein the amount of 2-(p,p''-bis(dimethylamino)benzhydrol)-5-dimethylaminobenzoic acid is from 2.5 to 10 percent by weight. 